In the motor industry, both 1-phase motors and 2-phase motors are referred to collectively as “single-phase motors.” However, the term single-phase motor will be used herein to mean phase 1 motors only, and excludes phase 2 motors.
Brushless motors that utilize permanent magnets and magnetic coils are known from publications such as JP 2001-298982A, for example.
In this prior art electric motor, control is carried out using an on/off signal from a digital magnetic sensor. Specifically, the timing for reversing the polarity of the voltage applied to the magnetic coils is determined using an on/off signal from the digital magnetic sensor. A three-phase drive signal is often used as the drive signal.
Conventional brushless motors utilized a drive signal with two or more phases; none use a single-phase drive signal. The reason is related to the startup characteristics of a single-phase motor which will be discussed below.
A characteristic of single-phase motors is that the motor cannot be started up with the permanent magnets and coils stopped in direct opposition to one another. This position is known as the “deadlock point” or “dead point.” Thus, the startup method employed for an ordinary single-phase motor involves providing a secondary winding for the purpose of reliable startup, with current flowing to the secondary winding only during startup. In a certain type of single-phase motor, a capacitor is employed to differentiate the phases of the primary winding and the secondary winding.
In ordinary brushless motors on the other hand, a so-called inverter drive is employed. However, when a single-phase employing an inverter drive is started up, there is considerable current flow to the secondary winding and the capacitor during startup, creating the problem of susceptibility to damage of the switching elements or capacitor. Accordingly, a problem encountered in the prior art is the difficulty of configuring a single-phase motor as a brushless motor.